Driven by the allure of the iPad, tablet PCs will surpass Netbooks in sales in just two years, according to a report released Thursday by Forrester Research.

In the U.S. alone, the burgeoning tablet industry is expected to sell 20.4 million units in 2015 compared with just 3.5 million this year, a compound annual growth rate of 42 percent, says Forrester's report "The U.S. Consumer PC Market in 2015." By 2014, more people will use tablets than Netbooks, and by 2015, tablets will make up 23 percent of all PC sales, forecasts Forrester.

"Tablet growth will come at the expense of Netbooks, which have a similar grab-and-go media consumption and Web browsing use case as tablets but don't synchronize data across services like the iPad does," Forrester Research Analyst Sarah Rotman Epps said in a statement. "Consumers didn't ask for tablets. In fact, Forrester's data shows that the top features consumers say they want in a PC are a complete mismatch with the features of the iPad. But Apple is successfully teaching consumers to want this new device."

Though the industry is still debating how to define a tablet, Forrester believes it should be classified as a type of personal computer. Fueled by their growing interest in tablets, consumers will scoop up almost half a billion PCs between now and 2015, says the report, a rise in unit sales of 52 percent. Those numbers encompass computers in all their various forms--desktops, notebooks, Netbooks, and tablets.

Desktop sales will continue to slip over the next five years, dropping to 15.7 million units sold in 2015 from 18.7 million this year. But the desktop will still have a vital role thanks to a need for CPU-intensive tasks like playing games and watching and editing high-definition video.

By 2015, the U.S. PC market will be led by notebooks with a 42 percent market share, says Forrester. Tablets will grab 23 percent of the market, desktops 18 percent, and Netbooks will bring up the rear with a 17 percent share.

A report this week from DisplaySearch echoed a similar forecast, predicting that the iPad will lead tablets to increasingly carve out chunks of the market currently enjoyed by Netbooks.